This invention relates to aerial cargo delivery systems and to cargo restraint locks therefor.
Cargo drops by parachute from aircraft have been used extensively in military operations and disaster relief situations. In the usual parachute cargo delivery system, loaded cargo carriers, such as platforms or pallets, are guided for movement along the longitudinal axis of the aircraft between parallel rails secured to the aircraft floor. These pallets can be pulled backwardly out of the rear cargo receiving and delivery opening by a deployed parachute (i.e., the "airdrop mode"). During flight, they are restrained against forward and aft movement (i.e., the "logistics mode"). Desirably, such cargo planes also must be capable of loading or unloading cargo from or to trucks while on the ground and also must be capable of discharging cargo onto the ground as the aircraft accelerates over the ground surface (i.e., the "combat off-load mode"). Further, the capability must exist in such a system for in-flight jettison of pallets or platforms in emergency conditions.
In certain prior art aerial cargo delivery systems of this type, two spaces apart parallel restraint rails support and guide the cargo pallets or platforms for longitudinal movement within the aircraft. One rail is provided with airdrop locks (i.e., those which permit only aft movement of a pallet under the force exerted by a deployed parachute) which provide positive forward restraint and force responsive aft restraint. In this type of system, the airdrop locks are armed and engaged with the pallets while the aircraft is on the ground. Separate logistics locks (i.e., those which prevent both forward and aft movement during normal flight conditions) are carried on the other rail and provide both forward and aft positive restraint. These locks also are engaged with the pallets while the aircraft is on the ground. In the airdrop mode, the logistic locks are all disengaged while the aircraft is in-flight shortly before airdrop, leaving the airdrop locks to provide all forward and aft restraint until the parachute force applied attains a predetermined level. At this time the airdrop locks simultaneously release all the pallets. If it is necessary to return to the logistically-locked position, the logistics locks must be manually reengaged. However, the pallets may shift slightly while the logistic locks are disengaged, resulting in a skewed condition of the pallets on the rails. This makes reengagement of the logistic locks very difficult due to slot misalignment.
The airdrop locks typically used in the system described include a spring release which is tripped at a predetermined force threshold in response to application of a predetermined parachute force in order to release the airdrop locks, when in the airdrop mode. For multiple pallet airdrops, this force is distributed over and shared by multiple airdrop locks which are engaged, respectively, with indents formed in the cargo pallets. Since the pallets commonly include two or three indents which are engaged with separate airdrop locks, the force must be shared essentially equally among all the locks engaged with each pallet to ensure a predictable lock release sequence. Accordingly, the threshold release level of each airdrop lock is based upon equal distribution of aft forces among the airdrop locks. In many practical cases, however, such a force distribution is not attainable because of irregular indent spacing or pallet misalignment. As a consequence, one lock may be positively engaged with a pallet indent, while others intended for engagement with the same pallet are not. This one lock therefore bears a disproportionate share of the aft force applied. Since the spring or fuse release trips at a precise threshold release, this airdrop lock tends to release prematurely, even due to dynamic forces which appear during flight prior to airdrop. This is commonly referred to as "zippering."
A cargo handling system which combines the logistics and airdrop lock functions in a single rail is disclosed in application Ser. No. 961,359, filed Nov. 16, 1978 now abandoned and continuation Ser. No. 092,146 filed Nov. 7, 1979, now U.S. Pat. No. 4,241,890; issued Dec. 30, 1980, by R. E. Pearson, and assigned to the assignee of the present invention. This system therefore provides versatility and economies which surpass systems of the type described above. However, the use of deformable metallic fuses as the force threshold elements may tend to encourage "zippering" in some instances. Further, the foldable rails, although sectional, must all be in their upright positions for operation of the locks by a sectional drawbar carried by the rail sections. Consequently, the aircraft equipped with this system is incapable of carrying both palletized and non-palletized cargo at the same time. Finally, as in the system of the type described above, this system releases all pallets simultaneously when operated in the airdrop mode. It therefore lacks the ability to drop one or more pallets from a group of pallets at selected times during, for example, multiple pass airdrops.